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• Name for Osherove's modified singleton pattern?

  - by Kazark

  I'm pretty well sold on the "singletons are evil" line of thought. Nevertheless, there are limited occurrences when you want to limit the creation of an object. Roy Osherove advises, If you're planning to use a singleton in your design, separate the logic of the singleton class and the logic that makes it a singleton (the part that initializes a static variables, for example) into two separate classes. That way, you can keep the single responsibility principle (SRP) and also have a way to override singleton logic. (The Art of Unit Testing 261-262) This pattern still perpetuates the global state. However, it does result in a testable design, so it seems to me to be a good pattern for mitigating the damage of a singleton. However, Osherove does not give a name to this pattern; but naming a pattern, according to the Gang of Four, is important: Naming a pattern immediately increases our design vocabulary. It lets us design at a higher level of abstraction. (3) Is there a standard name for this pattern? It seems different enough from a standard singleton to deserve a separate name. Decoupled Singleton, perhaps?

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• Entity system in Lua, communication with C++ and level editor. Need advice.

  - by Notbad

  Hi!, I know this is a really difficult subject. I have been reading a lot this days about Entity systems, etc... And now I'm ready to ask some questions (if you don't mind answering them) because I'm really messed. First of all, I have a 2D basic editor written in Qt, and I'm in the process of adding entitiy edition. I want the editor to be able to receive RTTI information from entities to change properties, create some logic being able to link published events to published actions (Ex:A level activate event throws a door open action), etc... Because all of this I guess my entity system should be written in scripting, in my case Lua. In the other hand I want to use a component based design for my entities, and here starts my questions: 1) Should I define my componentes en C++? If I do this en C++ won't I loose all the RTTI information I want for my editor?. In the other hand, I use box2d for physics, if I define all my components in script won't it be a lot of work to expose third party libs to lua? 2) Where should I place the messa system for my game engine? Lua? C++?. I'm tempted to just have C++ object to behave as servers, offering services to lua business logic. Things like physics system, rendering system, input system, World class, etc... And for all the other things, lua. Creation/Composition of entities based on components, game logic, etc... Could anyone give any insight on how to accomplish this? And what aproach is better?. Thanks in advance, HexDump.

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• How to implement behavior in a component-based game architecture?

  - by ghostonline

  I am starting to implement player and enemy AI in a game, but I am confused about how to best implement this in a component-based game architecture. Say I have a following player character that can be stationary, running and swinging a sword. A player can transit to the swing sword state from both the stationary and running state, but then the swing must be completed before the player can resume standing or running around. During the swing, the player cannot walk around. As I see it, I have two implementation approaches: Create a single AI-component containing all player logic (either decoupled from the actual component or embedded as a PlayerAIComponent). I can easily how to enforce the state restrictions without creating coupling between individual components making up the player entity. However, the AI-component cannot be broken up. If I have, for example, an enemy that can only stand and walk around or only walks around and occasionally swing a sword, I have to create new AI-components. Break the behavior up in components, each identifying a specific state. I then get a StandComponent, WalkComponent and SwingComponent. To enforce the transition rules, I have to couple each component. SwingComponent must disable StandComponent and WalkComponent for the duration of the swing. When I have an enemy that only stands around, swinging a sword occasionally, I have to make sure SwingComponent only disables WalkComponent if it is present. Although this allows for better mix-and-matching components, it can lead to a maintainability nightmare as each time a dependency is added, the existing components must be updated to play nicely with the new requirements the dependency places on the character. The ideal situation would be that a designer can build new enemies/players by dragging components into a container, without having to touch a single line of engine or script code. Although I am not sure script coding can be avoided, I want to keep it as simple as possible. Summing it all up: Should I lob all AI logic into one component or break up each logic state into separate components to create entity variants more easily?

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• How should I implement multiple threads in a game? [duplicate]

  - by xerwin

  This question already has an answer here: Multi-threaded games best practices. One thread for 'logic', one for rendering, or more? 6 answers So I recently started learning Java, and having a interest in playing games as well as developing them, naturally I want to create game in Java. I have experience with games in C# and C++ but all of them were single-threaded simple games. But now, I learned how easy it is to make threads in Java, I want to take things to the next level. I started thinking about how would I actually implement threading in a game. I read couple of articles that say the same thing "Usually you have thread for rendering, for updating game logic, for AI, ..." but I haven't (or didn't look hard enough) found example of implementation. My idea how to make implementation is something like this (example for AI) public class AIThread implements Runnable{ private List<AI> ai; private Player player; /*...*/ public void run() { for (int i = 0; i < ai.size(); i++){ ai.get(i).update(player); } Thread.sleep(/* sleep until the next game "tick" */); } } I think this could work. If I also had a rendering and updating thread list of AI in both those threads, since I need to draw the AI and I need to calculate the logic between player and AI(But that could be moved to AIThread, but as an example) . Coming from C++ I'm used to do thing elegantly and efficiently, and this seems like neither of those. So what would be the correct way to handle this? Should I just keep multiple copies of resources in each thread or should I have the resources on one spot, declared with synchronized keyword? I'm afraid that could cause deadlocks, but I'm not yet qualified enough to know when a code will produce deadlock.

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• Coherence Data Guarantees for Data Reads - Basic Terminology

  - by jpurdy

  When integrating Coherence into applications, each application has its own set of requirements with respect to data integrity guarantees. Developers often describe these requirements using expressions like "avoiding dirty reads" or "making sure that updates are transactional", but we often find that even in a small group of people, there may be a wide range of opinions as to what these terms mean. This may simply be due to a lack of familiarity, but given that Coherence sits at an intersection of several (mostly) unrelated fields, it may be a matter of conflicting vocabularies (e.g. "consistency" is similar but different in transaction processing versus multi-threaded programming). Since almost all data read consistency issues are related to the concept of concurrency, it is helpful to start with a definition of that, or rather what it means for two operations to be concurrent. Rather than implying that they occur "at the same time", concurrency is a slightly weaker statement -- it simply means that it can't be proven that one event precedes (or follows) the other. As an example, in a Coherence application, if two client members mutate two different cache entries sitting on two different cache servers at roughly the same time, it is likely that one update will precede the other by a significant amount of time (say 0.1ms). However, since there is no guarantee that all four members have their clocks perfectly synchronized, and there is no way to precisely measure the time it takes to send a given message between any two members (that have differing clocks), we consider these to be concurrent operations since we can not (easily) prove otherwise. So this leads to a question that we hear quite frequently: "Are the contents of the near cache always synchronized with the underlying distributed cache?". It's easy to see that if an update on a cache server results in a message being sent to each near cache, and then that near cache being updated that there is a window where the contents are different. However, this is irrelevant, since even if the application reads directly from the distributed cache, another thread update the cache before the read is returned to the application. Even if no other member modifies a cache entry prior to the local near cache entry being updated (and subsequently read), the purpose of reading a cache entry is to do something with the result, usually either displaying for consumption by a human, or by updating the entry based on the current state of the entry. In the former case, it's clear that if the data is updated faster than a human can perceive, then there is no problem (and in many cases this can be relaxed even further). For the latter case, the application must assume that the value might potentially be updated before it has a chance to update it. This almost aways the case with read-only caches, and the solution is the traditional optimistic transaction pattern, which requires the application to explicitly state what assumptions it made about the old value of the cache entry. If the application doesn't want to bother stating those assumptions, it is free to lock the cache entry prior to reading it, ensuring that no other threads will mutate the entry, a pessimistic approach. The optimistic approach relies on what is sometimes called a "fuzzy read". In other words, the application assumes that the read should be correct, but it also acknowledges that it might not be. (I use the qualifier "sometimes" because in some writings, "fuzzy read" indicates the situation where the application actually sees an original value and then later sees an updated value within the same transaction -- however, both definitions are roughly equivalent from an application design perspective). If the read is not correct it is called a "stale read". Going back to the definition of concurrency, it may seem difficult to precisely define a stale read, but the practical way of detecting a stale read is that is will cause the encompassing transaction to roll back if it tries to update that value. The pessimistic approach relies on a "coherent read", a guarantee that the value returned is not only the same as the primary copy of that value, but also that it will remain that way. In most cases this can be used interchangeably with "repeatable read" (though that term has additional implications when used in the context of a database system). In none of cases above is it possible for the application to perform a "dirty read". A dirty read occurs when the application reads a piece of data that was never committed. In practice the only way this can occur is with multi-phase updates such as transactions, where a value may be temporarily update but then withdrawn when a transaction is rolled back. If another thread sees that value prior to the rollback, it is a dirty read. If an application uses optimistic transactions, dirty reads will merely result in a lack of forward progress (this is actually one of the main risks of dirty reads -- they can be chained and potentially cause cascading rollbacks). The concepts of dirty reads, fuzzy reads, stale reads and coherent reads are able to describe the vast majority of requirements that we see in the field. However, the important thing is to define the terms used to define requirements. A quick web search for each of the terms in this article will show multiple meanings, so I've selected what are generally the most common variations, but it never hurts to state each definition explicitly if they are critical to the success of a project (many applications have sufficiently loose requirements that precise terminology can be avoided).

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• Entity Framework in n-layered application - Lazy loading vs. Eager loading patterns

  - by Marconline

  Hi all. This questions doesn't let me sleep as it's since one year I'm trying to find a solution but... still nothing happened in my mind. Probably you can help me, because I think this is a very common issue. I've a n-layered application: presentation layer, business logic layer, model layer. Suppose for simplicity that my application contains, in the presentation layer, a form that allows a user to search for a customer. Now the user fills the filters through the UI and clicks a button. Something happens and the request arrives to presentation layer to a method like CustomerSearch(CustomerFilter myFilter). This business logic layer now keeps it simple: creates a query on the model and gets back results. Now the question: how do you face the problem of loading data? I mean business logic layer doesn't know that that particular method will be invoked just by that form. So I think that it doesn't know if the requesting form needs just the Customer objects back or the Customer objects with the linked Order entities. I try to explain better: our form just wants to list Customers searching by surname. It has nothing to do with orders. So the business logic query will be something like: (from c in ctx.CustomerSet where c.Name.Contains(strQry) select c).ToList(); now this is working correctly. Two days later your boss asks you to add a form that let you search for customers like the other and you need to show the total count of orders created by each customer. Now I'd like to reuse that query and add the piece of logic that attach (includes) orders and gets back that. How would you front this request? Here is the best (I think) idea I had since now. I'd like to hear from you: my CustomerSearch method in BLL doesn't create the query directly but passes through private extension methods that compose the ObjectQuery like: private ObjectQuery<Customer> SearchCustomers(this ObjectQuery<Customer> qry, CustomerFilter myFilter) and private ObjectQuery<Customer> IncludeOrders(this ObjectQuery<Customer> qry) but this doesn't convince me as it seems too complex. Thanks, Marco

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• Network communication for a turn based board game

  - by randooom

  Hi all, my first question here, so please don't be to harsh if something went wrong :) I'm currently a CS student (from Germany, if this info is of any use ;) ) and we got a, free selectable, programming assignment, which we have to write in a C++/CLI Windows Forms Application. My team, two others and me, decided to go for a network-compatible port of the board game Risk. We divided the work in 3 Parts, namely UI, game logic and network. Now we're on the part where we have to get everything working together and the big question mark is, how to get the clients synchronized with each other? Our approach so far is, that each client has all information necessary to calculate and/or execute all possible actions. Actually the clients have all information available at all, aside from the game-initializing phase (add players, select map, etc.), which needs one "super-client" with some extra stuff to control things. This is the standard scenario of our approach: player performs action, the action is valid and got executed on the players client action is sent over the network action is executed on the other clients The design (i.e. no or code so far) we came up with so far, is something like the following pseudo sequence diagram. Gui, Controller and Network implement all possible actions (i.e. all actions which change data) as methods from an interface. So each part can implement the method in a way to get their job done. Example with Action(): On the player side's Client: Player-->Gui.Action() Gui-->Controller.Action() Controller-->Logic.Action (Logic.Action() == NoError)? Controller-->Network.Action() Network-->Parser.ParseAction() Network.Send(msg) On all other clients: Network.Recv(msg) Network-->Parser.Deparse(msg) Parser-->Logic.Action() Logic-->Gui.Action() The questions: Is this a viable approach to our task? Any better/easier way to this? Recommendations, critique? Our knowledge (so you can better target your answer): We are on the beginner side, in regards to programming on a somewhat larger projects with a small team. All of us have some general programming experience and basic understanding of the .Net Libraries and Windows Forms. If you need any further information, please feel free to ask.

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• Fake ISAPI Handler to serve static files with extention that are rewritted by url rewriter

  - by developerit

  Introduction I often map html extention to the asp.net dll in order to use url rewritter with .html extentions. Recently, in the new version of www.nouvelair.ca, we renamed all urls to end with .html. This works great, but failed when we used FCK Editor. Static html files would not get serve because we mapped the html extension to the .NET Framework. We can we do to to use .html extension with our rewritter but still want to use IIS behavior with static html files. Analysis I thought that this could be resolve with a simple HTTP handler. We would map urls of static files in our rewriter to this handler that would read the static file and serve it, just as IIS would do. Implementation This is how I coded the class. Note that this may not be bullet proof. I only tested it once and I am sure that the logic behind IIS is more complicated that this. If you find errors or think of possible improvements, let me know. Imports System.Web Imports System.Web.Services ' Author: Nicolas Brassard ' For: Solutions Nitriques inc. http://www.nitriques.com ' Date Created: April 18, 2009 ' Last Modified: April 18, 2009 ' License: CPOL (http://www.codeproject.com/info/cpol10.aspx) ' Files: ISAPIDotNetHandler.ashx ' ISAPIDotNetHandler.ashx.vb ' Class: ISAPIDotNetHandler ' Description: Fake ISAPI handler to serve static files. ' Usefull when you want to serve static file that has a rewrited extention. ' Example: It often map html extention to the asp.net dll in order to use url rewritter with .html. ' If you want to still serve static html file, add a rewritter rule to redirect html files to this handler Public Class ISAPIDotNetHandler Implements System.Web.IHttpHandler Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest ' Since we are doing the job IIS normally does with html files, ' we set the content type to match html. ' You may want to customize this with your own logic, if you want to serve ' txt or xml or any other text file context.Response.ContentType = "text/html" ' We begin a try here. Any error that occurs will result in a 404 Page Not Found error. ' We replicate the behavior of IIS when it doesn't find the correspoding file. Try ' Declare a local variable containing the value of the query string Dim uri As String = context.Request("fileUri") ' If the value in the query string is null, ' throw an error to generate a 404 If String.IsNullOrEmpty(uri) Then Throw New ApplicationException("No fileUri") End If ' If the value in the query string doesn't end with .html, then block the acces ' This is a HUGE security hole since it could permit full read access to .aspx, .config, etc. If Not uri.ToLower.EndsWith(".html") Then ' throw an error to generate a 404 Throw New ApplicationException("Extention not allowed") End If ' Map the file on the server. ' If the file doesn't exists on the server, it will throw an exception and generate a 404. Dim fullPath As String = context.Server.MapPath(uri) ' Read the actual file Dim stream As IO.StreamReader = FileIO.FileSystem.OpenTextFileReader(fullPath) ' Write the file into the response context.Response.Output.Write(stream.ReadToEnd) ' Close and Dipose the stream stream.Close() stream.Dispose() stream = Nothing Catch ex As Exception ' Set the Status Code of the response context.Response.StatusCode = 404 'Page not found ' For testing and bebugging only ! This may cause a security leak ' context.Response.Output.Write(ex.Message) Finally ' In all cases, flush and end the response context.Response.Flush() context.Response.End() End Try End Sub ' Automaticly generated by Visual Studio ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable Get Return False End Get End Property End Class Conclusion As you see, with our static files map to this handler using query string (ex.: /ISAPIDotNetHandler.ashx?fileUri=index.html) you will have the same behavior as if you ask for the uri /index.html. Finally, test this only in IIS with the html extension map to aspnet_isapi.dll. Url rewritting will work in Casini (Internal Web Server shipped with Visual Studio) but it’s not the same as with IIS since EVERY request is handle by .NET. Versions First release

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• My architecture has a problem with views that required information from different objects. How can I solve this?

  - by Oscar

  I am building an architecture like this: These are my SW layers ______________ | | | Views | |______________| ______________ | | |Business Logic| |______________| ______________ | | | Repository | |______________| My views are going to generate my HTML to be sent to the user Business logic is where all the business logics are Repository is a layer to access the DB My idea is that the repository uses entities (that are basically the representation of the tables, in order to perform DB queries. The layers communicate between themselves using Business Objects, that are objects that represent the real-world-object itself. They can contain business rules and methods. The views build/use DTOs, they are basically objects that have the information required to be shown on the screen. They expect also this kind of object on actions and, before calling the business logic, they create BO. First question: what is your overall feeling about this architecture? I've used similar architecture for some projects and I always got this problem: If my view has this list to show : Student1, age, course, Date Enrolled, Already paid? It has information from different BO. How do you think one should build the structure? These were the alternatives I could think of: The view layer could call the methods to get the student, then the course it studies, then the payment information. This would cause a lot of DB accesses and my view would have the knowledge about how to act to generate this information. This just seems wrong for me. I could have an "adapter object", that has the required information (a class that would have a properties Student, Course and Payment). But I would required one adapter object for each similar case, this may get very bad for big projects. I still don't like them. Would you have ideas? How would you change the architecture to avoid this kind of problems? @Rory: I read the CQRS and I don't think this suits my needs. As taken from a link references in your link Before describing the details of CQRS we need to understand the two main driving forces behind it: collaboration and staleness That means: many different actors using the same object (collaboration) and once data has been shown to a user, that same data may have been changed by another actor – it is stale (staleness). My problem is that I want to show to the user information from different BO, so I would need to receive them from the service layer. How can my service layer assemble and deliver this information? Edit to @AndrewM: Yes, you understood it correctly, the original idea was to have the view layer to build the BOs, but you have a very nice point about the creation of the BO inside the business layers. Assuming I follow your advice and move the creation logic inside the business layer, my business layer interface would contain the DTOs, for instance public void foo(MyDTO object) But as far as I understand, the DTO is tightly coupled to each view, so it would not be reusable by a second view. In order to use it, the second view would need to build a specific DTO from a specific view or I would have to duplicate the code in the business layer. Is this correct or am I missing something?

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• How to handle payment types with varying properties in the most elegant way.

  - by Byron Sommardahl

  I'm using ASP.NET MVC 2. Keeping it simple, I have three payment types: credit card, e-check, or "bill me later". I want to: choose one payment type display some fields for one payment type in my view run some logic using those fields (specific to the type) display a confirmation view run some more logic using those fields (specific to the type) display a receipt view Each payment type has fields specific to the type... maybe 2 fields, maybe more. For now, I know how many and what fields, but more could be added. I believe the best thing for my views is to have a partial view per payment type to handle the different fields and let the controller decide which partial to render (if you have a better option, I'm open). My real problem comes from the logic that happens in the controller between views. Each payment type has a variable number of fields. I'd like to keep everything strongly typed, but it feels like some sort of dictionary is the only option. Add to that specific logic that runs depending on the payment type. In an effort to keep things strongly typed, I've created a class for each payment type. No interface or inherited type since the fields are different per payment type. Then, I've got a Submit() method for each payment type. Then, while the controller is deciding which partial view to display, it also assigns the target of the submit action. This is not elegant solution and feels very wrong. I'm reaching out for a hand. How would you do this?

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• How do you handle 'SelectedItemChanged' events in a MVVM ViewModel?

  - by Travis

  I have some logic that depends upon two properties being set, as it executes when both properties have a value. For example: private void DoCalc() { if (string.IsNullOrEmpty(Property1) || string.IsNullOrEmpty(Property2)) return; Property3 = Property1 + " " + Property2; } That code would need to be executed every time Property1 or Property2 changed, but I'm having trouble figuring out how to do it in a stylistically acceptable manner. Here are the choices as I see them: 1) Call method from ViewModel I don't have a problem with this conceptually, as the logic is still in the ViewModel - I'm not a 'No code-behind' nazi. However, the 'trigger' logic (when either property changes) is still in the UI layer, which I don't love. The codebehind would look like this: void ComboBox_Property1_SelectedItemChanged(object sender, RoutedEventArgs e) { viewModel.DoCalc(); } 2) Call method from Property Setter This approach seems the most 'pure', but it also seems ugly, as if the logic is hidden. It would look like this: public string Property1 { get {return property1;} set { if (property1 != value) { property1 = value; NotifyPropertyChanged("Property1"); DoCalc(); } } } 3) Hook into the PropertyChanged event I'm now thinking this might be the right approach, but it feels weird to hook into the property changed event in the implementing viewmodel. It would look something like this: public ViewModel() { this.PropertyChanged += new PropertyChangedEventHandler(ViewModel_PropertyChanged); } void ViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e) { if (e.PropertyName == "Property1" || e.PropertyName == "Property2") { DoCalc(); } } So, my question is, if you were browsing through some source code with that requirement, which approach would you prefer to see implemented (and why?). Thanks for any input.

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• Please help with my JSP Internationalization problem

  - by wokena

  I have problem with I18N in JSP, specifically, with forms. When I enter some Czech characters (e.g., "ešcržýá...") into my page one form, into the field "fieldOne", and then show text from that field on page two, instead of Czech characters I see this as "čč". (Note, the second page gets the Czech characters with "request.getProperty("fieldOne")") Here is the source code: Page one: <%@page contentType="text/html"%> <%@page pageEncoding="UTF-8"%> <%@ taglib uri="http://jakarta.apache.org/struts/tags-bean" prefix="bean" %> <%@ taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html" %> <%@ taglib uri="http://jakarta.apache.org/struts/tags-logic" prefix="logic" %> <html> <head></head> <body> <form action="druha.jsp" method="post"> <input type="textarea" name="fieldOne"> <input type="submit"> </form> </body> </html> Page two: <%@page contentType="text/html" pageEncoding="UTF-8"%> <%@ taglib uri="http://jakarta.apache.org/struts/tags-bean" prefix="bean" %> <%@ taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html" %> <%@ taglib uri="http://jakarta.apache.org/struts/tags-logic" prefix="logic" %> <html> <head></head> <body> <h1>The text: </h1> <%=request.getProperty("fieldOne")%> </body> </html> Thanks for help...

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• Why is Dispatcher.Invoke not triggering UI update?

  - by Brandon

  I am trying to reuse a UserControl and also borrow some logic that keeps track of progress. I'll try and simplify things. MyWindow.xaml includes a MyUserControl. MyUserControl has its own progress indicator (Formatting in progress..., Copying files..., etc.) and I'd like to mirror this progress somewhere in the MyWindow form. But, the user control has some logic I don't quite understand. I've read and read but I still don't understand the Dispatcher. Here's a summary of the logic in the user control that updates the progress. this.Dispatcher.Invoke(DispatcherPriority.Input, (Action)(() => { DAProgressIndicator = InfiniteProgress.AddNewInstanceToControl(StatusGrid, new SolidColorBrush(new Color() { A = 170, R = 128, G = 128, B = 128 }), string.Empty); DAProgressIndicator.Message = MediaCardAdminRes.ActivatingCard; ActivateInProgress = true; })); I thought I'd be smart and add an event to MyUserControl that would be called in the ActivateInProgress property set logic. public bool ActivateInProgress { get { return _activateInProgress; } set { _activateInProgress = value; if (ActivateInProgressHandler != null) { ActivateInProgressHandler(value); } } } I'm setting the ActivateInProgressHandler within the MyWindow constructor to the following method that sets the view model property that is used for the window's own progress indicator. private void SetActivation(bool activateInProgress) { viewModel.ActivationInProgress = activateInProgress; } However, the window's progress indicator never changes. So, I'm convinced that the Dispatcher.Invoke is doing something that I don't understand. If I put a message box inside the SetActivation method, the thread blocks and the window's progress indicator is updated. I understand basic threads but this whole Dispatcher thing is new to me. What am I missing?

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• General N-Tier Architecture Question

  - by whatispunk

  In an N-Tier app you're supposed to have a business logic layer and a data access layer. Is it bad to simply have two assemblies: BusinessLogicLayer.dll and DataAccessLayer.dll to handle all this logic? How do you actually represent these layers. It seems silly, the way I've seen it, to have a BusinessLogic class library containing classes like: CustomerBusinessLogic.cs, OrderBusinessLogic.cs, etc. each calling their appropriately named cousin in the DataAccessLayer class library, i.e. CustomerDataAccess.cs, OrderDataAccess.cs. I want to create a web app using MVP and it doesn't seem so cut and dry as this. There are lots of opinions about where the business logic is supposed to be put in MVP and I'm not sure I've found a really great answer yet. I want this project to be easily testable, and I am trying to adhere to TDD methodologies as best I can. I intend to use MSTest and Rhino Mocks for testing. I was thinking of something like the following for my architecture: I'd use LINQ-To-SQL to talk to the database. WCF services to define data contract interfaces for the business logic layer. Then use MVP with ASP.NET Forms for the UI/BLL. Now, this isn't the start of this project, most of the LINQ stuff is already done, so its stuck. The WCF service would replace the existing DataAccessLayer assembly and the UI/BLL would replace the BusinessLogicLayer assembly etc. This sort of makes sense in my head, but its getting really late. Anyone that's traveled down this path have any guidance? Good links? Warnings? Thanks!

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• Naming convention for non-virtual and abstract methods

  - by eagle

  I frequently find myself creating classes which use this form (A): abstract class Animal { public void Walk() { // TODO: do something before walking // custom logic implemented by each subclass WalkInternal(); // TODO: do something after walking } protected abstract void WalkInternal(); } class Dog : Animal { protected override void WalkInternal() { // TODO: walk with 4 legs } } class Bird : Animal { protected override void WalkInternal() { // TODO: walk with 2 legs } } Rather than this form (B): abstract class Animal { public abstract void Walk(); } class Dog : Animal { public override void Walk() { // TODO: do something before walking // custom logic implemented by each subclass // TODO: walk with 4 legs // TODO: do something after walking } } class Bird : Animal { public override void Walk() { // TODO: do something before walking // custom logic implemented by each subclass // TODO: walk with 2 legs // TODO: do something after walking } } As you can see, the nice thing about form A is that every time you implement a subclass, you don't need to remember to include the initialization and finalization logic. This is much less error prone than form B. What's a standard convention for naming these methods? I like naming the public method Walk since then I can call Dog.Walk() which looks better than something like Dog.WalkExternal(). However, I don't like my solution of adding the suffix "Internal" for the protected method. I'm looking for a more standardized name. Btw, is there a name for this design pattern?

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• How does a java web project architecture look like without EJB3 ?

  - by Hendrik

  A friend and I are building a fairly complex website based on java. (PHP would have been more obvious but we chose for java because the educational aspect of this project is important to us) We have already decided to use JSF (with richfaces) for the front end and JPA for the backend and so far we have decided not to use EJB3 for the business layer. The reason we've decided not to use EJB3 is because - and please correct me if I am wrong - if we use EJB3 we can only run it on a full blown java application server like jboss and if we don't use EJB3 we can still run it on a lightweight server like tomcat. We want to keep speed and cost of our future web server in mind. So far i've worked on two JEE projects and both used the full stack with web business logic factories/persistence service entities with every layer a seperate module. Now here is my question, if you dont use EJB3 in the business logic layer. What does the layer look like? Please tell what is common practice when developing java web projects without ejb3? Do you think business logic layer can be thrown out altogether and have business logic in the backing beans? If you keep the layer, do you have all business methods static? Or do you initialize each business class as needed in the backing beans in every session as needed?

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• Authenticated WCF: Getting the Current Security Context

  - by bradhe

  I have the following scenario: I have various user's data stored in my database. This data was entered via a web app. We'd like to expose this data back to the user over a web service so that they can integrate their data with their applications. We would also like to expose some business logic over these services. As such we do not want to use OData. This is a multi-tenant application so I only want to expose their data back to them and not other users. Likewise, the business logic we expose should be relative to the authenticated user. I would like let the user use an OASIS scheme to authenticate with the web service -- WCF already allows for this out of the box as far as I understand -- or perhaps we can issue them certificates to authenticate with. That bit hasn't really been worked out yet. Here is a bit of pseudo-code of how I envision this would work within the service: function GetUsersData(id) var user := Lookup User based on Username from Auth Context var data := Get Data From Repository based on "user" return data end function For the business logic scenario I think it would look something like this: function PerformBusinessLogic(someData) var user := Lookup User based on Username from Auth Context var returnValue := Perform some logic based on supplied data return returnValue end function The hard bit here is getting the current username (or cert info in the cert scenario) that the user authenticated with! Does WCF even enable this scenario? If not would WSE3 enable this? Thanks,

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• Error of iterator in mys JSP

  - by Mercer

  Hello, in my jsp i do this <table> <tr> <th>TITLLE</th> </tr> <tr class="row0"> <logic:iterate id="listClient" name="Client"> <td> [...] </td> </logic:iterate> </tr> </table> <logic:iterate id="listClient" name="Client"> <table> <tr> <td> [...] </td> </tr> </table> </logic:iterate> But i have this error for my second iterate javax.servlet.jsp.JspException: Cannot create iterator for this collection

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• Flex/Flash 4 ExternalInterface.call - trying to get a string from HTML to Actionscript.

  - by Setori

  Dear all, I need to obtain a string from HTML and put it into Actionscript. the actionscript: import flash.external.ExternalInterface; protected function getUserName():void{ var isAvailable:Boolean = ExternalInterface.available; var findUserName:String = "findUserName"; if(isAvailable){ var foundUserName:String = ExternalInterface.call(findUserName); Alert.show(foundUserName);}} the javascript: function findUserName() { var label = document.getElementById("username-label"); if(label.value != ""){ alert("the name in the box is: " + label.value); return label.value;} else return "nothing in the textbox";}} the JSP: <%IUserSession userSession = SessionManager.getSession();%> <logic:notEmpty name="userSession"> <logic:notEqual value="anonymous" name="userSession" property="userLoginId"> <td align="right" width="10%" > <input id="username-label" type="text" value="<bean:write name="userSession" property="userLoginId"/>" /> </td> </logic:notEqual> </logic:notEmpty> the rendered HTML: <td align="right" width="10%"> <input id="username-label" type="text" value="a-valid-username" /> </td> when the javascript execution hits var label = document.getElementById("username-label"); a null is returned and crashes, no alert shows no error message is shown. firfox 3.5 windows, container is Tomcat. Please advise, and thank you in advance.

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• When is it better to use a method versus a property for a class definition?

  - by ccomet

  Partially related to an earlier question of mine, I have a system in which I have to store complex data as a string. Instead of parsing these strings as all kinds of separate objects, I just created one class that contains all of those objects, and it has some parser logic that will encode all properties into strings, or decode a string to get those objects. That's all fine and good. This question is not about the parser itself, but about where I should house the logic for the parser. Is it a better choice to put it as a property, or as a method? In the case of a property, say public string DataAsString, the get accessor would house the logic to encode all of the data into a string, while the set accessor would decode the input value and set all of the data in the class instance. It seems convenient because the input/output is indeed a string. In the case of a method, one method would be Encode(), which returns the encoded string. Then, either the constructor itself would house the logic for the decoding a string and require the string argument, or I write a Decode(string str) method which is called separately. In either case, it would be using a method instead of a property. So, is there a functional difference between these paths, in terms of the actual running of the code? Or are they basically equivalent and it then boils down to a choice of personal preference or which one looks better? And in that kind of question... which would look cleaner anyway?

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• What is the best practice in regards to building composite dtos off of an aggregate root with domain

  - by Chance

  I'm trying to figure out the best approach/practice for assembling a composite data transfer object off of an aggregate root and would love to hear people's thoughts on this. For example, lets say I have a root that has a few domain objects as children. I want to assemble a specific view dto, based on some business logic, that either has attributes or full dto's of it's objects. What I'm struggling with is trying to figure out where that assembly should happen. I can see it going on the domain object of the aggregate root as there is some business logic associated with it. The benefits of this approach from what I've deduced thus far is that it should reduce the inevitable business logic from bleeding outisde of the domain object. It also allows for private methods that take care of tasks that could become more complex from an external builder. The downsides being that the domain object becomes much more entrenched in the application's workflow and represents much more than just the domain object. It also could become very large in the scenario where you need multiple composite Dtos. Alternatively, I could also see it belonging to some form of transfer object assembler where there is a builder for each domain object. The domain objects would still be responsible for GetDto() and UpdateFromDto(dto). Outside of that, the builder would handle the construction and deconstruction of composite dtos. The downside is kind of mentioned above, where I fear this will easily lead to developers unfamiliar with DDD bleeding a ton of business logic into the assembler which is what I want to desperately avoid. Any thoughts would be greatly apperciated.

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• JavaScript Keycode 46 is DEL Function key or (.) period sign?

  - by Omar

  Im writing some logic in JavaScript using jquery, where i must check the input content against a REGEX pattern ex: "^[a-zA-Z0-9_]*$" //Alpha-numeric and _ The logic is almost done, i just have a little problem filtering the function key DEL, my logic goes like this: var FunctionsKey = new Array(8, 9, 13, 16, 35, 36, 37, 39, 46); function keypressValidation(key) { if (config.regexExp != null) { if ($.inArray(key, FunctionsKey) != -1) { return true; } else { var keyChar = String.fromCharCode(key); return RegexCheck(keyChar); } } return true; } If the KeyCode is one of those in the array, i let it pass, if not i get the char and compare it against the REGEX. The problem is: in some Browsers the DEL and '.' (period sign) have the same key Code 46. So is there a better logic to filter the function keys or must i write a condition for that case, maybe removing the 46 from the array and try to convert it to char and if is (.) let it go to the Regex function if not let it pass? The other question will be are there more shared Key Codes in some browsers? EDIT: My suggested solution wont work because it doesn't matter which key the user pressed (DEL or period) i always get (.) as CHAR at least on OPERA and FF =(.

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• What kind of data do I pass into a Django Model.save() method?

  - by poswald

  Lets say that we are getting POSTed a form like this in Django: rate=10 items= [23,12,31,52,83,34] The items are primary keys of an Item model. I have a bunch of business logic that will run and create more items based on this data, the results of some db lookups, and some business logic. I want to put that logic into a save signal or an overridden Model.save() method of another model (let's call it Inventory). The business logic will run when I create a new Inventory object using this form data. Inventory will look like this: class Inventory(models.Model): picked_items = models.ManyToManyField(Item, related_name="items_picked_set") calculated_items = models.ManyToManyField(Item, related_name="items_calculated_set") rate = models.DecimalField() ... other fields here ... New calculated_items will be created based on the passed in items which will be stored as picked_items. My question is this: is it better for the save() method on this model to accept: the request object (I don't really like this coupling) the form data as arguments or kwargs (a list of primary keys and the other form fields) a list of Items (The caller form or view will lookup the list of Items and create a list as well as pass in the other form fields) some other approach? I know this is a bit subjective, but I was wondering what the general idea is. I've looked through a lot of code but I'm having a hard time finding a pattern I like.

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• Looking for an appropriate design pattern

  - by user1066015

  I have a game that tracks user stats after every match, such as how far they travelled, how many times they attacked, how far they fell, etc, and my current implementations looks somewhat as follows (simplified version): Class Player{ int id; public Player(){ int id = Math.random()*100000; PlayerData.players.put(id,new PlayerData()); } public void jump(){ //Logic to make the user jump //... //call the playerManager PlayerManager.jump(this); } public void attack(Player target){ //logic to attack the player //... //call the player manager PlayerManager.attack(this,target); } } Class PlayerData{ public static HashMap<int, PlayerData> players = new HashMap<int,PlayerData>(); int id; int timesJumped; int timesAttacked; } public void incrementJumped(){ timesJumped++; } public void incrementAttacked(){ timesAttacked++; } } Class PlayerManager{ public static void jump(Player player){ players.get(player.getId()).incrementJumped(); } public void incrementAttacked(Player player, Player target){ players.get(player.getId()).incrementAttacked(); } } So I have a PlayerData class which holds all of the statistics, and brings it out of the player class because it isn't part of the player logic. Then I have PlayerManager, which would be on the server, and that controls the interactions between players (a lot of the logic that does that is excluded so I could keep this simple). I put the calls to the PlayerData class in the Manager class because sometimes you have to do certain checks between players, for instance if the attack actually hits, then you increment "attackHits". The main problem (in my opinion, correct me if I'm wrong) is that this is not very extensible. I will have to touch the PlayerData class if I want to keep track of a new stat, by adding methods and fields, and then I have to potentially add more methods to my PlayerManager, so it isn't very modulized. If there is an improvement to this that you would recommend, I would be very appreciative. Thanks.

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• Basic Application Organization + Publishing (.NET 4.0)

  - by keynesiancross

  Hi all, I'm trying to figure out the best way to keep my program organized. Currently I have many class files in one project file, but some of these classes do things that are very different, and some I would like to expose to other applications in the future. One thought I had to organizing my application was to create multiple project files, with one "Main" project, which would interact with all the other projects and their relevant classes as needed. Does this make sense? I was wondering if anyone had any suggestions in regards to using multiple project files in one solution (and how do you create something like this?), and if it makes sense to have multiple namespaces in one solution... Cheers ----Edit Below---- Sorry, my fault. Currently my program is all in one console project. Within this project I have several classes, some of which basically launch a BackgroundWorker and run an endless loop pulling data. The BackgroundWorker then passes this data back to the main business logic as needed. I'm hoping to seperate this data pull material (including the background worker material) into one project file, and the rest of the business logic into another project file. The projects will have to pass objects between eachother though (the data to the main business logic, and the business logic will pass startup parameteres to the dataPull project)... Hopefully this adds a bit more detail.

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